1. Field of the Invention
The present invention relates to a motorcycle of a type which drives a rear wheel using a drive shaft.
2. Description of Background Art
There has been known a motorcycle which mounts a rear swing arm on a vehicle body frame in a rockable manner by way of a support portion, pivotally supports a rear wheel on a rear portion of the rear swing arm, and includes a drive shaft which drives the rear wheel (for example, see JP-A-2002-87364 (FIG. 4)
FIG. 4 of JP-A-2002-87364 is a back view of a pivotally supporting portion of a rear arm, wherein a rear arm bracket 7 is mounted on a rear portion of a main frame 6, and a rear arm 14 (hereinafter, referred to as a rear swing arm 14) is mounted on the rear arm bracket 7 by way of a pivot shaft 10.
The rear swing arm 14 has a head portion 14c at a front end thereof and the head portion 14c is squeezed to have a narrow width. In the same manner, the pivot shaft 10 is also formed with a small length. Such a constitution is necessary for arranging a universal joint portion 42 (hereinafter, referred to as the universal joint 42) on a side of the pivot shaft 10.
With respect to a twisting force which acts on the rear swing arm 14, the larger the width of the head portion 14c or the larger the length of the pivot shaft 10, it is possible to increase the supporting rigidity.
In this respect, the head portion 14c has the small width and the pivot shaft 10 is short in JP-A-2002-87364 and hence, it is necessary for the rear swing arm 14 to increase the diameter of the head portion 14c or the diameter of the pivot shaft 10 to ensure the supporting rigidity. As a result, the weight of the swing arm 14 is increased.